1. Field of the Invention
The present invention relates to coil components incorporated in, for example, electronic circuits, and more particularly, to a multilayer coil component used in a high-frequency circuit.
2. Description of the Related Art
A typical coil component incorporated in an electronic circuit of, for example, a cellular phone is shown in FIG. 12.
As shown in FIG. 12, a coil component 100 includes a multi-turn spiral pattern 101 disposed on an insulating layer 102, and an insulating layer 103 stacked on the spiral pattern 101. The insulating layer 103 includes an extending portion 104 thereon, which is connected to the spiral pattern 101 through a via hole 105.
Improvements in miniaturization and high inductance in coil components are in great demand in compliance with compactness of mobile communication devices, such as cellular phones. However, with the coil component 100 having the multi-turn spiral pattern 101 within a single layer, a sufficient number of turns for achieving high inductance cannot be obtained due to space limitations.
Consequently, a technology for obtaining a small-size high-inductance coil component by forming multilayer spiral patterns has been proposed, as shown in FIG. 13.
A coil component 200 shown in FIG. 13 is a multilayer type that includes two spiral patterns 201, 202 connected to each other in series in a stacking direction.
In detail, the first spiral pattern 201 is provided on the insulating layer 102, and the second spiral pattern 202 is provided on the insulating layer 103. Central portions of the spiral patterns 201, 202 are connected to each other through the via hole 105.
In this case, although the multilayer spiral pattern coil provides a sufficient number of turns and high inductance, the coil component 200 has higher stray capacitance as comparison to the coil component 100 shown in FIG. 12. In particular, a stray capacitance value produced in an outer peripheral portion of the coil is extremely high.
For example, as shown in FIG. 13, a line extending from an outermost periphery point P1 of the spiral pattern 201 to a point P2 of the spiral pattern 202 corresponding to the point P1 is equal to a sum of a path extending between the point P1 and a central portion 201a of the spiral pattern 201 and a path extending between a central portion 202a of the spiral pattern 202 and the point P2, such that the line is extremely long. Thus, a potential difference between the point P1 and the point P2 is large, and therefore, stray capacitance C200 produced between the point P1 and the point P2 is high. Such an increase in stray capacitance value leads to a decrease in self-resonance frequency of the coil component 200, thus deteriorating the high frequency property of the coil component 200.
In contrast, a multilayer coil component 300 that prevents an increase in stray capacitance has been proposed, as shown in FIG. 14 (see, for example, Japanese Unexamined Patent Application Publication No. 55-096605 (Patent Document 1) and Japanese Unexamined Patent Application Publication No. 5-291044 (Patent Document 2)).
The coil component 300 includes a pattern group 301 disposed on the insulating layer 102, and the insulating layer 103 stacked on the pattern group 301. The pattern group 301 includes rectangular annular patterns 311 to 316 that have overlapping opposite end segments and that are arranged substantially concentrically on the insulating layer 102. The coil component 300 also includes a pattern group 302 having rectangular annular patterns 321 to 326 that are arranged substantially concentrically on the insulating layer 103. The annular patterns 321 to 326 have non-overlapping end segments that are separated by a predetermined distance. First ends of the annular patterns 321 to 326 are connected to first ends of the annular patterns 311 to 316 through corresponding via holes 105a to 105j provided in the insulating layer 103.
Accordingly, for example, a line extending from an outermost peripheral point P1 of the pattern group 301 to a point P2 of the pattern group 302 corresponding to the point P1 is equal to a sum of a path extending between the point P1 and an end 311a of the annular pattern 311 and a path extending between an end 321a of the annular pattern 321 and the point P2, such that the line is extremely short. Therefore, a potential difference between the point P1 and the point P2 is small, whereby stray capacitance C300 produced between the point P1 and the point P2 is low.
However, although the stray capacitance can be reduced in the coil component 300 shown in FIG. 14, a sufficient number of turns for achieving high inductance cannot be obtained.
In other words, since the opposite end segments of the annular patterns 311 to 316 are arrayed in an overlapping manner, each annular pattern requires an area for disposing the corresponding opposite end segments in the arrayed direction of the opposite end segments (i.e. in a front direction closer to the viewer of FIG. 14). Therefore, due to space limitations, a sufficient number of annular patterns 311 to 316 cannot be obtained, which prevents the pattern group 301 from having a sufficient number of turns. Consequently, it is difficult to achieve high inductance of the coil component 300.